Movable brace frame for self-installing platform

ABSTRACT

Pre-assembled self installing platforms with improved performance due to additional rotational restraint to supporting legs and methods of installation. The platform includes a hull, legs movable relative to the hull, at least one brace frame movably connected to at least two of the legs. Upon installation, the brace frame may be positioned at a desired elevation and rigidly secured to the legs, providing rotational restraint to significantly reduce leg stress and increase rigidity of the legs. With the increased rigidity, it becomes possible to install platforms in relatively deep waters and harsh environments, and yet preventing large overall platform sway induced by adverse weather or sea conditions. As the brace frame is securable to the legs after the legs or footings are penetrated into or supported on the sea bed, differential penetration of legs or footings into the seabed becomes possible without risking large structural loads in the brace frame.

BACKGROUND

1. Technical Field

Embodiments of the invention relate generally to apparatus and methodsfor improving the in place performance of a self-installing platform.

2. Description of Related Art

Various methods of installing offshore platforms are available but haveinherent problems.

One conventional method of installing fixed offshore platforms requireslarge floating cranes to lift and install a jacket structure onto theseabed, and subsequently lift and install a topside structure onto theinstalled jacket structure. This method is expensive due to limitedavailability and high operational and rental costs of the large floatingcranes.

Alternative to using large floating cranes, self-installing platformshave been developed. These self-installing platforms may be completelyassembled at the yard and include movable legs which can be moved up anddown relative to the hull using a (temporary) jacking system. The legsare disposed in a raised position during tow and are lowered once theplatform is at the offshore site.

One type of self-installing platform has a relatively light steel trussstructure to support topside structures. The self-installing platformsmay be transported by a barge which provides enhanced sea keepingcharacteristics during tow. The hull structure is supported by legswhich are not interconnected, thereby resulting in a very flexiblesupporting structure. Accordingly, the platform can only be installed inrelative shallow water and/or benign environments.

Another type of self-installing platform includes interconnected legswhich provide a much stiffer supporting structure. Accordingly, theplatform can be installed in deeper waters and/or harsher environments,unlike a platform without interconnected legs. However, it is notpossible to tow the platform on a barge as the presence of a bargesupporting the platform would prevent lowering of the interconnectedlegs. As such, the platform has to be specially designed to take thehydrostatic loads during tow and the small freeboard during tow rendersthe platform susceptible to green water. Further, when the legs areinterconnected, the acceptable differential seabed penetration of thefootings is within very narrow limits. If the differential penetrationis too large, the bracings interconnecting the legs would experiencelarge structural loads. Consequently, this type of self-installingplatform can only be installed on a flat seabed.

Canadian Patent No. 1,117,301 (Evans, Darrell L.) discloses aself-contained jack up type drilling and production platform structurecomprising a floatable barge-like hull with support legs which can bejacked up and down to lower and raise the hull with respect to thesurface of the sea. A removable drilling module rests on top of the hulland extends over an opening therein between two of the support legs.Production equipment is arranged in the hull and communicates with theopening. Moveable conductor supports extend between the legs of theplatform and serve to brace the drill string and production conduitconductors. However, the movable conductor supports are meant to supportthe drill string and production conduit conductors, and would notimprove the performance of the support legs.

U.S. Pat. No. 4,245,928 (Nei et al.) discloses a method for theconstruction of a structure sufficiently reinforced particularly againsta lateral force by driving the desired number of pile members into thewater and integrally connecting these pile members with the bracemembers. The connection of the pile members with the brace members isaccomplished by providing a gap between the brace and pile members, andfilling the gap with a filler joining material having a powerful bondingforce, such as an expansive mortar. The connecting work is devised to beperformed safely and accurately on the surface of the water. However,various components of the structure have to be assembled at the offshoresite which is a time-consuming and expensive process requiring floatingcranes, and is therefore not a desirable alternative.

U.S. Pat. No. 2,837,897 (Nedderman et al.) relates one of its objects asproviding an automatic underwater bracing system which is initiallycollapsed but which is automatically erected between the supportingcolumns as they are being lowered to bottom. The bracing system isprimarily used to tension the cables connected to the bracing system sothat the tensioned cables provide stiffness to the support structure.

U.S. Pat. No. 3,593,529 (Smulders) discloses a buoyant mobile drillingplatform having a gap in its side in which is detachably disposed apermanent drilling platform. The two platforms are floated to thedrilling site and temporarily emplaced. If a test drill shows thepresence of gas or oil, then the permanent platform is permanentlyemplaced and the mobile platform is floated away.

SUMMARY

Embodiments of the invention relate to pre-assembled self-installingplatforms which are provided with rotational restraint. A pre-assembledself-installing platform may include a hull, a plurality of supportinglegs which are movable relative to the hull, and at least one braceframe which is movably connected to at least two of the plurality oflegs and is securable to the at least two of the plurality of legs.

The self-installing platform may be pre-assembled before beingtransported to an offshore site for installation. At the offshore site,the plurality of legs of the self-installing platform may be loweredinto the seabed. The brace frame may then be positioned at a desiredelevation along the at least two of the plurality of legs and securedthereto. This way, rotational restraint is provided to significantlyreduce leg stress and increase rigidity of the legs. With the increasedrigidity, it has become possible to install platforms in relatively deepwaters and harsh environments, and yet preventing large overall platformsway induced by adverse weather or sea conditions. As the brace frame issecurable to the legs after the legs or footings are penetrated into orsupported on the sea bed, differential penetration of legs or footingsinto the seabed is possible without risking large structural loads inthe brace frame.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are disclosed hereinafter with reference tothe drawings, in which:

FIG. 1A illustrates a self-installing platform with a movable braceframe during transportation according to one embodiment of theinvention;

FIG. 1B illustrates a self-installing platform of FIG. 1A afterinstallation;

FIG. 2 is a close-up view of a leg and brace frame connection of aself-installing platform with grouting;

FIG. 3A illustrates a self-installing platform having a movable braceframe movably coupled to the legs using a rack and pinion system;

FIG. 3B illustrates a leg and brace frame connection of FIG. 3A in anunsecured arrangement;

FIG. 3C illustrates a leg and brace frame connection of FIG. 3A in asecured arrangement;

FIG. 4A illustrates a self-installing platform with two movable braceframes during transportation according to one embodiment of theinvention;

FIG. 4B illustrates a self-installing platform of FIG. 4A afterinstallation;

FIG. 5 is a top view of a movable brace frame according to oneembodiment of the invention;

FIG. 6 illustrates a self-installing platform having a movable braceframe formed of a truss structure according to one embodiment of theinvention; and

FIGS. 7A to 7D illustrate a sequence for installing a self-installingplatform according to one embodiment of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of various illustrativeembodiments of the invention. It will be understood, however, to oneskilled in the art, that embodiments of the invention may be practicedwithout some or all of these specific details. In other instances, wellknown process operations have not been described in detail in order notto unnecessarily obscure pertinent aspects of embodiments beingdescribed. In the drawings, like reference numerals refer to same orsimilar functionalities or features throughout the several views.

According to embodiments of the invention, in which a platform includesa hull and supporting legs, at least one brace frame is provided whichis movable along at least two legs of a platform and securable to thelegs at any elevation. Upon securing the brace frame to the legs thatprovide a support structure to the platform, the brace frame providesrotational restraint to the legs, thus resulting in significantlyreduced stress in the legs and a more rigid supporting structure. Thiswould allow installation of platforms in relatively deep waters andharsh environments, and yet preventing large overall platform sway.

Reference is made to FIGS. 1A and 1B which illustrate a self-installingplatform 10, according to one embodiment of the invention, duringtransportation (or tow) and after installation respectively. The hull 12is illustrated as a truss structure for supporting topside modules (notshown) thereon. It is to be appreciated that the hull 12 may be formedof other suitable structures including, but not limited to, a barge typebuoyant hull.

The supporting legs 14 of the self-installing platform 10 are movablerelative to the hull 12 and adjustable between at least a raised (orstowed) position and a lowered (or installed) position depending on theoperational status of the self-installing platform 10. Particularly, thelegs 14 may be disposed for independent vertical movement relative tothe hull 12, such as by using a jacking system provided on the hull. InFIGS. 1A and 1B, through holes are provided in the hull 12 for receivingthe legs 14 and allowing the legs 14 to be lowered or raised. Duringtransportation (FIG. 1A), the legs 14 are stowed in a raised position inwhich the legs 14 may be partially supported by the hull 12. The hull 12may, in turn, be supported on a barge 40. Additionally, the legs 14 maybe secured to the barge 40 or hull 12 during transportation to fixedlyarrange the legs 14 in the raised position. During installation (FIG.1B), the legs 14 are lowered relative to the hull 12 into an installedposition in which the legs 14 support the hull 12. Additionally, thelegs 14 may be secured to the hull 12 to fixedly arrange the legs 14 inthe installed position.

In FIGS. 1A and 1B, the self-installing platform 10 includes four legs14 of tubular type. In certain other embodiments of the invention, aself-installing platform 10 may have other number of legs 14, rangingfrom three and above. Also, the legs 14 may take other forms including,but not limited to, rectangular hollow section, square truss andtriangular truss.

At bottom ends of the legs 14, footings 16 may be provided to providesufficient bearing when the legs 14 are anchored to the seabed 55.Examples of suitable footings include, but are not limited to, suctioncans, spud cans, and piled footings. At top ends of the legs 14, legheads, having a cross-section larger than the legs 14 and the throughholes receiving the legs 14, may be provided. Further, after the legs 14are lowered into an installed position, the legs 14 may be secured tothe hull 12, such as by bolts.

Rotational restraint of the legs 14 may be provided to increasestiffness and rigidity of the support structure of the self-installingplatform 10 in the installed position. Particularly, at least one braceframe 20 may be provided to connect at least two legs 14 at one or moreelevations. The at least one brace frame 20 is movable along the legs 14to be positioned at one or more desired elevations. Once the brace frame20 is secured to the legs 14, rotational restraint is provided to thelegs 14 to significantly reduce leg stresses and increase rigidity ofthe supporting structure of the self-installing platform 10. With thisincreased rigidity, it has now become possible to install platforms inrelatively deep waters and harsh environments, and yet preventing largeoverall platform sway induced by adverse weather or sea conditions.Accordingly, the rotational restraint provided to the legs 14 orsupporting structure of a self-installing platform improves the in placeperformance of the self-installing platform.

In one embodiment of the invention, a brace frame 20 may include sleeves22, as shown in FIG. 2, fitted around each of two or more legs 14 of theself-installing platform 10. Adjacent sleeves 22 are connected by bracemembers 24 to form a brace frame 20. The brace frame 20 is movablycoupled to the legs 14 to allow positioning at any desired elevationalong the legs 14. For this purpose, cables 36 (or cable system) incooperation with winches or strand jacks (not shown) may be provided onthe hull 12 and coupled to the brace frame 20 for lowering and raisingthe brace frame 20. After the brace frame 20 is positioned at a desiredelevation, the brace frame 20 may be secured to the legs 14 to provide arigid connection in a horizontal plane. In one example, the brace frame20 may be secured to the legs 14 by grouting with a suitable fillerjoining or grout material 32 (see FIG. 2) or by a mechanical connectionincluding, but not limited to, clamps. Further, guides (not shown) maybe disposed within the sleeves 22 to prevent the sleeves 22 fromscratching the legs 14 during lowering or raising of the brace frame 20.

It is to be appreciated that other devices for lowering and raising thebrace frame 20 may be employed. In one embodiment of the invention asillustrated by FIGS. 3A to 3C, a rack and pinion system is provided forpositioning the brace frame 20 along the legs 14. Particularly, rackrailways 26 are mounted along the legs 14 while pinions 28 are mountedto the brace frame 20. The pinions 28 are disposed in movable engagementwith the rack railways 26. To raise or lower the brace frame 20, thepinions 28 may be actuated by a power source in either rotationaldirection as required. FIG. 3B illustrates the brace frame 20 in anunsecured or unlocked arrangement in which clamps 34 are disengaged withthe rack railways 26. After the brace frame 20 is positioned at adesired elevation, the brace frame 20 may be rigidly secured to the legs14. For this purpose, clamps 34 with compatible teeth configuration asthe rack railway 26 are moved into locking engagement with the rackrailways 26. FIG. 3C illustrates the brace frame 20 in a secured orlocked arrangement in which clamps 34 are arranged in locking engagementwith the rack railways 26. This way, the brace frame 20 is preventedfrom undesirable movements and is rigidly secured to the legs 14.

While a single brace frame 20 is provided in FIGS. 1A and 1B, it is tobe appreciated that two or more brace frames 20 may be secured to thelegs 14 at different elevations for providing increased rigidity. FIGS.4A and 4B illustrate a self-installing platform 10 with two brace frames20 in a tow position and an installed position respectively.

In addition, while FIGS. 1A and 1B illustrate a brace frame 20 havingbrace members 24 forming a square configuration, other configurationsmay be envisaged. For example, FIG. 5 illustrates a brace frame 20having brace members 24 forming a square and a cross configuration.

Further, while FIGS. 1A and 1B illustrate brace members 24 in tubularform, the brace members 24 may take other forms including, but notlimited to, rectangular hollow section, square truss and triangulartruss. FIG. 6 illustrates a brace frame 20 formed of a truss structure.

A method for installing a platform at an offshore site, without use of afloating crane, is described with reference to FIGS. 7A to 7D. Aself-installing platform 10 may be pre-assembled at a yard. Theself-installing platform 10 may comprise a hull 12, legs 14 forsupporting the hull 12 and at least one brace frame 20 movably coupledto at least two of the legs 14. Other components may be pre-assembled ifrequired. The pre-assembled self-installing platform 10 may betransported to an offshore site by a barge 40 which may be towed byanother vessel (see FIG. 7A for a side view of a barge 40 supporting apre-assembled self-installing platform 10). Particularly, the hull 12 issupported on the barge 40 with legs 14 of the self-installing platform10 arranged in a raised position and alongside the barge 40. The braceframe 20 may be interposed between the hull 12 and the barge 40. Thelegs 14 of the self-installing platform 10 may be secured to the barge40 during transportation. Footings 16 of the legs 14 may be disposedbelow the barge 40 or under the water surface 50 and pulled against thebarge 40.

After reaching the desired offshore site, the legs 14 may beindividually or simultaneously lowered until the footings 16 of the legs14 come into supporting contact with a seabed 55 or are penetrated intothe seabed 55 (see FIG. 7B). Suitable equipment including, but notlimited to, strand jacks may be used for lowering and raising the legs14 and other components. In certain embodiments, the footings 16 may beinterconnected by a temporary frame (not shown) such that the positionsof the footings 16 are fixed in a horizontal plane and would notdisplace relative to one another during lowering onto the seabed. Thiswould prevent the footings 16 from penetrating the seabed with arelative offset which would cause difficulties subsequently whenlowering the brace frame 20. After the footings 16 have penetrated theseabed, the temporary frame may be removed.

After the footings 16 are suitably supported on or penetrated into theseabed, the hull 12 and brace frame 20 may be raised relative to thelegs 14 to provide sufficient clearance from the barge 40 (see FIG. 7C)so that the barge 40 may be floated away from the self-installingplatform 10. The brace frame 20 may then be lowered to a desiredposition, such as by lowering cables 36 coupled to the brace frame 20(see FIG. 7D) or by a rack and pinion system. After the brace frame 20is positioned at the desired position, the brace frame 20 may be rigidlysecured to the legs 14, such as by a grout material 32 or by clamps 34.

Using a barge for transporting the self-installing platform providesstability and enhanced sea keeping characteristics during tow, and alsominimises risk of green water, i.e. relatively compact mass of waterflowing onto platform, which would cause damage to the platform and anytopside modules thereon. However, in certain other embodiments of theinvention, the pre-assembled self-installing platform may be floated toan offshore site without assistance of a barge. In this connection, thehull of the self-installing platform may be formed of a buoyantstructure.

Other variations to the above-described method may also be envisaged.For example, the brace frame may be supported below the barge duringtransportation. The footings may be disposed alongside the barge duringtransportation. Depending on the topology of the seabed, the footingsmay have equal penetration where the seabed is relatively even or havedifferential penetration if the seabed is undulating. An advantage ofthe brace frame, according to embodiments of the invention, is that asecured connection between a leg and a brace frame is made after theplatform is installed on-site. This necessarily means that differentialpenetration would not introduce structural loads in the brace frame.This is in contrast with certain other types of self-installingplatforms with interconnected legs, where differential penetration ofsupport legs will result in considerable structural loads in theinterconnecting bracings.

A method for uninstalling the platform may be performed as follows. Thesecured connection between the brace frame and legs may be removed. Themovable brace frame may be raised to a suitable height so that a bargemay be moved under the hull of the platform and the brace frame (see forexample FIG. 7C). The hull and the movable brace may be supported on thebarge while the legs may be lifted into a raised position. The legs maybe secured to the barge which then transports the platform to adestination, e.g. another offshore site, or yard.

Other embodiments will be apparent to those skilled in the art fromconsideration of the specification and practice of the invention.Furthermore, certain terminology has been used for the purposes ofdescriptive clarity, and not to limit the disclosed embodiments of theinvention. The embodiments and features described above should beconsidered exemplary, with the invention being defined by the appendedclaims.

1. A pre-assembled self-installing platform comprising: a hull; aplurality of legs movable relative to the hull; and at least one braceframe movably connected to at least two of the plurality of legs,wherein the at least one brace frame is securable to the at least two ofthe plurality of legs for providing rotational restraint thereto.
 2. Thepre-assembled self-installing platform of claim 1, wherein the at leastone brace frame further includes: a plurality of sleeves fitted aroundthe at least two of the plurality of legs; and at least one brace memberconnecting the plurality of sleeves.
 3. The pre-assembledself-installing platform of claim 1, wherein the at least one braceframe includes a truss structure.
 4. The pre-assembled self-installingplatform of claim 1, wherein the at least one brace frame is securableto the at least two of the plurality of legs by one of a filler joiningmaterial and a clamp.
 5. The pre-assembled self-installing platform ofclaim 1, further comprising: a plurality of guides interposed betweenthe plurality of sleeves and the at least two of the plurality of legsfor preventing scratching on the at least two of the plurality of legs.6. The pre-assembled self-installing platform of claim 1, furthercomprising: a rack and pinion system for movably connecting the at leastone brace frame with the at least two of the plurality of legs; and aplurality of clamps for securing the brace frame to the at least two ofthe plurality of legs at a desired elevation.
 7. A method for installinga platform, comprising: transporting a pre-assembled self-installingplatform to an offshore site, the pre-assembled self-installing platformcomprising: a hull; a plurality of legs movable relative to the hull,and at least one brace frame movably connected to at least two of theplurality of legs, wherein the at least one brace frame is securable tothe at least two of the plurality of legs for providing rotationalrestraint thereto; lowering the plurality of legs into a seabed;positioning the at least one brace member at a desired elevation alongthe at least two of the plurality of legs; and securing the at least onebrace member to the at least two of the plurality of legs.
 8. The methodof claim 7, wherein transporting a pre-assembled self-installingplatform further includes transporting by a barge supporting thepre-assembled self-installing platform.
 9. The method of claim 7,wherein transporting a pre-assembled self-installing platform furtherincludes floating the pre-assembled self-installing platform.
 10. Themethod of claim 7, wherein positioning the at least one brace memberfurther includes lowering the at least one brace member using one of acable system and a rack and pinion system.
 11. The method of claim 7,wherein securing the at least one brace member to the at least two ofthe plurality of legs further includes securing using one of a fillerjoining material and a clamp.